67 lines
2.3 KiB
Diff
67 lines
2.3 KiB
Diff
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From 45c5960cecfa238f87f94c7d9803d9216f40ca12 Mon Sep 17 00:00:00 2001
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From: Thomas Gleixner <tglx@linutronix.de>
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Date: Tue, 9 May 2017 17:11:10 +0200
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Subject: [PATCH 180/365] futex/rtmutex: Cure RT double blocking issue
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RT has a problem when the wait on a futex/rtmutex got interrupted by a
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timeout or a signal. task->pi_blocked_on is still set when returning from
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rt_mutex_wait_proxy_lock(). The task must acquire the hash bucket lock
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after this.
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If the hash bucket lock is contended then the
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BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on)) in
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task_blocks_on_rt_mutex() will trigger.
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This can be avoided by clearing task->pi_blocked_on in the return path of
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rt_mutex_wait_proxy_lock() which removes the task from the boosting chain
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of the rtmutex. That's correct because the task is not longer blocked on
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it.
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Reported-by: Engleder Gerhard <eg@keba.com>
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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kernel/locking/rtmutex.c | 19 +++++++++++++++++++
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1 file changed, 19 insertions(+)
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diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
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index 42a91329b4cd..2674b3cfb70c 100644
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--- a/kernel/locking/rtmutex.c
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+++ b/kernel/locking/rtmutex.c
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@@ -2388,6 +2388,7 @@ int rt_mutex_wait_proxy_lock(struct rt_mutex *lock,
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struct hrtimer_sleeper *to,
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struct rt_mutex_waiter *waiter)
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{
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+ struct task_struct *tsk = current;
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int ret;
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raw_spin_lock_irq(&lock->wait_lock);
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@@ -2399,6 +2400,24 @@ int rt_mutex_wait_proxy_lock(struct rt_mutex *lock,
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* have to fix that up.
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*/
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fixup_rt_mutex_waiters(lock);
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+
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+ /*
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+ * RT has a problem here when the wait got interrupted by a timeout
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+ * or a signal. task->pi_blocked_on is still set. The task must
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+ * acquire the hash bucket lock when returning from this function.
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+ *
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+ * If the hash bucket lock is contended then the
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+ * BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on)) in
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+ * task_blocks_on_rt_mutex() will trigger. This can be avoided by
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+ * clearing task->pi_blocked_on which removes the task from the
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+ * boosting chain of the rtmutex. That's correct because the task
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+ * is not longer blocked on it.
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+ */
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+ if (ret) {
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+ raw_spin_lock(&tsk->pi_lock);
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+ tsk->pi_blocked_on = NULL;
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+ raw_spin_unlock(&tsk->pi_lock);
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+ }
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raw_spin_unlock_irq(&lock->wait_lock);
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return ret;
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--
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2.28.0
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